Reduction of steel billets or blooms in a steel mill to a finished product (e.g. rod or wire) is a time consuming and expensive operation involving the use of costly equipment.
Typically, a billet is reduced to a work product which becomes longer and longer with each pass. Because of the elongation involved in the reduction of the billet, the bar or rod may be cropped into smaller lengths which can be processed individually without requiring the whole billet work product to pass through and be stored on coiling apparatus at either side of the reduction rollers.
In order to reduce the quantity of steel product which must be passed through the reduction stages of a reducing rolling mill, operators have sought methods of slitting a reduced billet into a plurality of parallel sections after a predetermined number of passes (usually 10) in a primary reduction process. The work product is slit into two (usually) pieces which may be processed in a parallel finishing operation, as opposed to causing the work product to be completely finished in one continuous piece.
Typically, a well known prior art method of reduction employing a slitting operation in general use, at the present time, requires that a steel billet be reduced to a "fluted square" in a predetermined number of passes (usually 10) in a primary reduction mill.
The fluted square is rolled into what is generally referred to as a "dog bone" shape which is reduced to a "peanut" shape in two rolling steps.
The peanut shape of the steel workpiece lends itself to slitting because of the narrow web holding the two substantially circular sections of the peanut together.
Thus, the single peanut is slit with two separate strands (or sections) which may be processed in a parallel reducing operation to yield a finished product.
Most steel mill operators agree that the use of a slitting operation is more efficient than employing rolling reduction to achieve the same reduction in cross sectional area of the workpiece.
But slitting, by means of the prior art, is not without ensuing problems. The process, just described, produces only two workpieces which may be processed by a parallel processing operation. If an attempt is made to increase the number of sections of separated parallel workpieces, problems may arise because of the adverse material flow in forming the hot steel workpiece. The adverse flow results from forcing the hot steel product to flow in directions other than the direction of rolling in order to produce the complex shape of the hot steel workpiece which is to be subsequently slit into four or five parallel sections. Problems also arise due to uneven temperature distribution in the resulting slitted workpieces which result in difficulty in subsequent rolling required to achieve the final shape in the finished product, resulting in the production of an inferior product.
The "dog bone"-"peanut" slitting operation itself requires moving the hot steel product through four rolling stands and (usually) eight separate mill guides, to successfully produce the separated product sections. A malfunction in any one of the eight guides may lead to an interruption in the production of the slitted workpiece. Those familiar with the process are well aware of the hostile nature of the environment in which these guiding devices must operate.
Methods other than the "dog bone"-"peanut" production procedures have been employed by steel mill operators with varying degrees of success.
At times, when the plurality of sections of different cross sectional area are formed in a workpiece prior to the actual slitting operation, the acceleration forces to which the various sections of the workpiece are subjected are sufficient to cause premature fracture of the web holding the sections together, or if the workpiece remains intact, it tends to undergo severe curvature as it exits from the rolling mill. Problems, arising from such operations, result in lower quality finished product and at times the generation of scrap.
Slitting with wedge shaped cutters may also produce an end product having undesirable camber (see U.S. Pat. No. 4,370,910) which may yield a section which is subsequently difficult to roll. As well, some rolling processes cause an adverse material flow in the web of the section being slit in a directions other than in the direction of rolling. This undesirable material flow in the web yields a product the physical characteristics of which may be somewhat impaired.
At other times, steel mill operators have developed sophisticated methods of twisting the hot steel product before it is passed into the slitter-rollers. The twisting of a hot steel product requires the use of equipment, which in prior art installations, is subject to wear and may be prone to failure because of the nature of the operation being carried out on the product passing through the mill. At other times, the slitting operation requires the addition of other rolling accessories to "straighten" the product.